Cardiac electrophysiological processes are distributed over the three-dimensional (3-D) volume of the heart. Such processes include excitation and relaxation of the heart. Attempts have been made to probe and image cardiac electrical activity from body surface electrocardiograms or magnetocardiograms, or from catheter recordings within blood cavities, for the purpose of aiding clinical diagnosis and management of cardiac diseases. While the endocardial recordings and non-contact inverse mapping techniques provide a minimally invasive means of localizing and mapping cardiac electrical activity over the endocardial surface, they may be limited when cardiac activation or repolarization inhomogeneity arise or occur from regions far from the endocardial surface.